DESCRIPTION: The major goal of the proposed research is to elucidate the cognitive and neural bases of working memory. By testing subjects with Alzheimer's disease (AD), Parkinson's disease (PD), or discrete lesions within frontal, temporal, or parietal cortex, and comparing them with normal control subjects (NCS), the investigators hope to define the neural networks that support working memory and to dissect the functional specialization of structure within it. Working memory relies on executive functions and may be organized into at least two independent subsystem, one for storing and manipulating memory for locations in space and one for storing and manipulating memory for the features of objects. This application will administer tests of working memory and tests of non-mnemonic cognitive operations that support working memory performance. These tests will manipulate spatial location, objects, words, encoding time, decision time, movement time, and retrieval time. Converging evidence about the neural substrate for these operations will be obtained from studies on patients and from fMRI imaging.